Whipstocks, in essence, are long ramps that direct a milling or drilling assembly laterally into a tubular wall to form an opening referred to as a window for a lateral exit from a main bore. These whipstocks have to be properly oriented so that the mill will exit in a desired orientation into the oilfield's producing or injection zone, depending on the application. Measurement while drilling (MWD) or wireline gyro tools assist in the orientation of the whipstock ramp before an underlying anchor is set for fixation of the whipstock.
Traditionally, prior art whipstocks have been used to drill deviated boreholes from an existing wellbore. A whipstock has a ramped surface that is set in a predetermined position to guide a drill bit or drill string in a deviated manner to drill into the side of the wellbore, which may also be called a sidetrack window or window. In operation, the whipstock is positioned, or set, on the bottom of the existing wellbore. The set position of the whipstock is then surveyed and the whipstock is properly oriented for directing a drill string in the proper direction. The direction of the drill string determines the production effort's ability to achieve the desired hydrocarbon resources extraction. After the whipstock is set, a drill string is lowered into the well to engage with the whipstock, thus causing the drill string to drill a deviated borehole through a wall of the existing wellbore.
Other uses for prior art whipstocks include sidetracking from previously drilled and cased/uncased wellbores that have become unproductive. For example, when a wellbore becomes unusable, a new borehole may be drilled in the vicinity of the existing cased or uncased wellbore. Alternatively, a new borehole may be sidetracked from the serviceable portion of the existing, cased or uncased wellbore. Sidetracking from a cased or uncased wellbore also may be useful for developing multiple production zones. This procedure can be accomplished by milling through the side of the casing and/or into the wellbore wall with a mill that is guided by a wedge or whipstock component. After a milling or drilling procedure is completed, the whipstock may be removed from the wellbore.
A currently available design for a known mechanically supported whipstock and anchor enables the running tool to engage a whipstock opening. Typically, the running tool has a hook that engages an opening in the whipstock ramp. A shear pin or bolt initially secures the running tool to the top of the ramp when running in. The running tool has an extension tube that runs through the whipstock body under the ramp and into a seal bore of a bottom sub connected below the ramp. An anchor may be located below bottom sub. The procedure with this design traditionally includes cementing through the anchor onto a support that exists in the borehole and that is not shown to create a barrier that may be requested by some operators. When cementing to create a barrier is concluded, a ball is dropped on a seat near the anchor to set the anchor. The prior art running tool may be then released by shearing a pin or bolt by setting down weight against the set anchor to get the hook out of an opening in the ramp, followed by rotating before pulling out of the hole with the running tool, so as to avoid re-engaging the hook in the opening on the way out of the hole.
First, the uncased portion of the wellbore needs to be cemented. In this known or prior art configuration, a cementing assembly may be connected to a drill string and run down the wellbore until it is positioned into an uncased portion of the wellbore. The entire wellbore may be uncased or the lower portion below the casing may be uncased. Cement is pumped down the drill string and out the assembly to cement the uncased portion of the wellbore. After cementing the uncased bore of a wellbore, the drill string may be removed from the wellbore and a mill may be run down the wellbore. When the mill is positioned adjacent to the newly cemented portion of the wellbore, the mill will be actuated and moved downward. The mill will continue to travel down the wellbore until it engages a whipstock, which changes the direction of the mill causing it to produce a sidetrack of the wellbore.
The repeated trips down the wellbore of the prior art devices in order to position the cementing assembly, remove the drill string, insert, orient and position the whipstock are time consuming and costly. It would be beneficial to reduce the amount of time required to perform the operation of cementing and subsequently sidetracking in the wellbore.
There are, thus, several limitations in this prior art process. One is that the known running tool may be positioned in a highly deviated portion of a borehole making rotation difficult and further reducing surface feedback as to how much rotation has actually taken place at the hook with a given amount of rotation at the surface. In a deviated borehole, rubbing on the wall can result in far less rotation at a downhole end of a string than the rotation applied at the surface.
The presently described running tool for use within a cementing whipstock assembly addresses the above known limitations of existing technologies. The benefits of this new running tool with a releasably-engaged cement tube for minimizing downhole trips during a cementing operation is here describe and claimed.